Toyota Sienna Forum - siennachat.com banner

1 - 11 of 11 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter #1
Greetings...

2002 Sienna CE with 200,000+ miles... Starting two months ago, I got code 0420. My O2 sensor data shows downstream sensor reading at less then the lower end of the expected range of 0.1-0.9 volts. Without truly understand the thing, I replaced the downstream O2 sensor. But the check engine light came back after about 60 miles. I then replaced the catalytic converter. But the code came back after about 50 miles of highway driving.

The attached pictures show the value is fully in range. So I'm completely puzzled over the code returning.

If the data is outside the spec range of 0.1 ~ 0.9volts, which end is more problematic? <0.1 or >0.9volts?



Would a more experienced have a look and point out what I should try next?
47125
 

·
Registered
Joined
·
883 Posts
If you still have the original A/F sensors, they aren't producing good output. But with the replacement cat, unless it's an OEM, you may be out of luck. The ECM is calibrated very strictly,and it's rarely the cat at fault.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #3
here the graph including the two OEM A/F sensors, with the original Cat and downstream O2 sensor (so please ignore the bottom two pictures). Do the A/F sensor output look good? The original CAT has to be bad as after the CAT replacement, I also put the old downstream O2 sensor back, it displays the same pattern as the new one.

The non-OEM CAT is declared to be "made-in Canada" quality, but cost just $93. My mechanic also said the same as you did. But Toyota doesn't even sell CAT, only the whole exhaust system.

But if a vendor declares a CAT as being for 1. Gen. Sienna, it has to work, right?

47142
 

·
Registered
Joined
·
166 Posts
The ECU sets the P0420 after the catalyst test fails. You would have to be looking at the O2 signal
while the ECU was actually running the test to see the values it is testing. From what I
remember reading, the ECU richens the mixture to for a time, and the leans it out for a short time.
It then compares the waveform from a front AF sensor to the rear O2 sensor. The rear O2 signal
must be different from the front AF sensor. This indicates that the cats are functioning and
"cleaning" the exhaust. There are actually 3 cats... 2 pre-cats... and then the final cat.
The pre-cats are small. One is built into the front manifold. The other is built into the y-pipe
that connects to the rear manifold.

I fought the P0420 several times. I tried aftermarket Walker and Bosal y-pipes. My P0420 code came
back after a few months. They are cheap for a reason. They have less of the expensive catalyst.
There is a TSB(EG047-05) concerning the P0420 code in the 2001-2003 Siennas. The original ECU cat
test is too stringent. An updated ECU is supposed to help fix this problem. But a dealer wants $1500 for
their mistake. They want about the same for 3 new cats. Being that your cats have 200K miles on
them, they are most likely used up.

I would first check to make sure that you don't have any leakage at the connections from the
exhaust manifolds to the pipes. These flanges uses "crush" gaskets that should not be reused.
I might have continued to get my P0420 code because I didn't always use a new gasket when
I replaced the y-pipe or final cat. Make sure no air is puffing by the gasket with a piece
of tissue paper on a stick. It's sometimes hard to tell with air coming from the engine fan.

I updated my ECU by finding a used ECU for $120. It however came from a Sienna with an immobilizer.
Mine did not have one. So I had to reprogram the immobilizer's 93c56 chip on the ECU motherboard
to a "virgin" state. After doing so, my Sienna ran... and the code was gone for about a year.
It finally came back again... and I was about to give up. My final solution was to install
the Radio Shack diode in the harness before the plug of the final O2 sensor. This attenuates the
signal from the final O2 sensor and makes the ECU see a difference in the waveform. The cat test
then passed for good after that.

A link to a post with the diode solution:
 

·
Registered
Joined
·
20 Posts
Discussion Starter #5
Wow! thanks Rob for sharing so much! I just ordered a Magnaflow California CARB and EPA compliant CAT, MAG447206, for cut and weld, but I'll use self-made clamps and copper tape instead.
What model year's Sienna ECU has the bug fixed? and no immobilier? How did you reprogram the chip? Before going that road, I will try your diode method first. will post my result at each try. starting with the CAT.

Is there a way to tell if the upstream A/F sensors could be bad?
 

·
Registered
Joined
·
883 Posts
If you haven't downloaded a repair manual yet, here's the P0420 section.

A bad A/F sensor should set a P1135/1155. "Should." My and others' vans' sensors failed in the 100-150,000-mile range.
 

Attachments

·
Registered
Joined
·
20 Posts
Discussion Starter #7 (Edited)
Thank you so much pkjsr02!

I'll do a full test following this sheets. where to get such a shop manual?

I replaced my three sensors at around 90,000 miles 10 years ago, that cleared the CEL. Since I didn't know which one was bad back then, I should have kept those sensors.
 

·
Registered
Joined
·
166 Posts
The ECU issue is for the 2001-2003 Siennas with the VVT. Since the ECUs are not "flashable", you have to replace them to get the firmware update. I found an updated ECU in a junkyard about a half an hour from my house! The updated ECU has a different part number. Attached is a PDF for the TSB that shows the updated part numbers. I found a 89661–08062 ECU for my 2001. No stock Siennas ever received the updated ECUs from the factory. The problem was addressed well after the 2003 generation ceased production. The date on the TSB is 2005.

I reprogrammed the 93C56 chip by buying a chip programmer and doing a lot of research to find the data to download into it. It is a simple 256 byte file. Here is where I posted it:

I un-soldered the tiny thing and soldered a new re-programmed chip back on. You have to be a good solderer to do this and not cross any circuits. I never could read or reprogram the chip properly when it was on the board. So I programmed a new chip and replaced it. Somewhere on the site is a post where I describe the process in more detail.
 

Attachments

·
Registered
Joined
·
20 Posts
Discussion Starter #9 (Edited)
thanks so much for sharing the bulletin! I wonder why Toyota didn't make it a full recall. I didn't know about it, so the 96 months warranty had passed for my Sienna.

I bought the 2002 vehicle when it was two years old in 2004, so I'm not sure if the ECU on it has been fixed, or reprogrammed. I'll see if I can see the part number on the device. A few weeks ago, I was thinking it might have reached a point of no return when things start breaking down one after another. But my wife loves the Sienna, she even drove with our 3 kids from NJ to the border of California last summer, a ~10,000 mile trip through many historical sites - when it was at 199,000 miles already, and after a bad rear crash that twisted the rear steel bumper, which I replaced with one from a junkyard, and plastic-welded the bumper cover, still visible on the signature photo :) . So it bears some emotional fruit of memory for the family.... Back home, I replaced the front lower control arms, stabilizer bar-links, and a new pair of front brake rotors, and rear brake shoes - a hard and fun job! So if I can overcome the 0420, I hope we can keep it for a few more years until the kids move out.

Today, I realized the air filter is completely dirty, and likely clogged too, just replaced it. To check the I have the luck a new air filter can have a little effect, I erased the code. Will observe a few more days before my MagnaFlow California and EPA compliant CAT arrives. If the CEL stays off, maybe even my old CAT is good after all - likely wishful thinking... will report back. - YES IT WAS, My pipe dream was broken when CEL came back after 42 miles. So I've got the use the California and EPA compliant CAT.

This is a fantastic forum! I am now a lot more knowledgeable than just two weeks ago.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #10
Just to report back to everyone in the thread. This last weekend, I installed the new MagnaFlow CARB and CA compliant CAT I ordered, and drove 100 miles today to pickup a piano for the kids. No more P0420! the CAT costs $200, and I can even get a refund of up to $75 by sending back the bad OEM CAT for recycling.
Without a welding machine, I used copper tape to increase the original pipe's OD, and used steel reinforced EPoxy mixed with steel wool in addition to make sure the fit is tight, and use a pair of self-made steel clamps. After installation, I added exhaust repair cement together with a round of copper wire. It's now as hard as rock. So there can be absolutely no leak. The original O2 sensor mounting bolts have rusted away, so I made a pair of hardware with L-shape steel from a kids' old ice-board to mount the sensor by turning it 90-degree. See picture. Hope that's enough for at least another 100k :)
47273
47274
 

·
Super Moderator
Joined
·
5,067 Posts
Nice repair job!

Recalls are mandated for two reasons: There is a safety concern, or in the case of an emissions problem the vehicles passes when it should have failed. Failing when it should pass (this case) is typically handed thru TSB and maybe a warranty extension, but not a recall. But I agree, owners should not have been thrown to the wolves because of a programming error that potentially makes their vehicle not pass a State Inspection and thus undriveable by law.
 
1 - 11 of 11 Posts
Top